RO 31-8959 is a transition state analogue of a characteristic HIV proteinase cleavage site. It acts by inhibiting an essential proteolysis of the gag and gag-pol proteins in newly forming HIV particles, which are thus kept in a noninfectious state. This study will compare the safety, tolerance and efficacy based on clinical endpoints of a comparison or combination of RO 31-8959 and ddC. Patients will be randomized in a double-blind manner to four parallel groups.